1. Field of the Invention
The present invention relates to a mounting mechanism of a process cartridge for an image forming apparatus comprising image forming process elements including an electrostatic member, a developing device, a corona charger, and a cleaning device.
2. Description of Related Art
An image forming apparatus comprising electrophotographic process elements such as an electrophotographic photosensitive member, a developing device, a corona charger, and a cleaning device has been known, as described in U.S. Pat. No. 4,878,548, in which the electrophotographic process elements are made into an integral process cartridge capable of being mounted on or removed from the main unit of the apparatus. The construction and operation of such an electrophotographic apparatus are explained in reference to FIGS. 6 through 9 of this application.
The electrophotographic apparatus comprises an automatic paper sheet feeder 4 and a manual paper sheet feeder 5. A paper sheet 6 is fed by either one of the paper sheet feeders 4 and 5 and guided to a pair of resist rollers 10 and 11 by paper sheet guides 7, 8, and 9 disposed downstream of the paper sheet feeders 4 and 5.
If a paper sheet detection sensor 12 disposed upstream of the pair of resist rollers 10 and 11 detects the passage of a paper sheet 6 and a predetermined period of time elapses from the time of detection, the pair of resist rollers 10 and 11 start to rotate. The paper sheet 6 with its skew feed corrected by the resist rollers 10 and 11 is fed downstream while being sandwiched between the rollers 10 and 11 according to the rotation of the rollers 10 and 11.
Paper sheet guides 13a and 13b are disposed in a confronting relationship with each other to form a paper sheet passage downstream of the resist rollers 10 and 11. The paper sheet 6 after being fed out of the resist rollers 10 and 11 is fed to an image forming section 50 while guided by the paper sheet guides 13a and 13b.
The image forming section 50 comprises an electrophotographic photosensitive member 15 having a drum base with electric conductivity and a photoconductive layer, a corona charger 20 for uniformly charging the electrophotographic photosensitive member 15, an exposure device 26 for projecting an optical image onto the electrophotographic photosensitive member 15, a developing device 21 holding toner therein for developing an electrostatic latent image formed by the projection, a transfer section 14 for transferring the developed, visualized toner image to the paper sheet 6, and a discharging section 16 for electrically discharging the paper sheet 6 after the transfer process and separating the paper sheet 6 from the electrophotographic photosensitive member 15.
The photosensitive member 15 is journaled to be rotatable in the direction of the arrow A. Around the photosensitive member 15, arranged in its rotating direction, are the corona charger 20, the exposure device 26, the developing device 21, the transfer section 14, the discharging section 16, and a cleaning device 22. The photosensitive member 15, the corona charger 20, the developing device 21, and the cleaning device 22 are constructed as an integral process unit 51.
After forming the image on the paper sheet 6 in the image forming section 50, the paper sheet 6 is guided over a guiding section 17 and transferred further downstream to a fixing device 18. After the image is fixed by heat and pressure of the fixing device 18 onto the paper sheet 6, the paper sheet 6 is sent out into a discharged paper sheet tray 27 by a pair of paper sheet discharge rollers 28 and 29.
The electrophotographic apparatus of the construction described above requires replacement of components of the image forming section 50 in the following situations. The developing device 21 has to be replaced when the toner is exhausted. The corona charger 20 requires replacement when the surfaces of charging wires become dirty with toner and dust. The cleaning device 22 must be replaced when toner deposits form thereon. The photosensitive member 15 requires replacement when its surface characteristic deteriorates.
The developing device 21, the corona charger 20 and the cleaning device 22 must be disposed within specified distances relative to the photosensitive member 15. Such distances, however, are changed if the developing device 21, the corona charger 20, and the cleaning device 22 are replaced individually. As a result, there has been a problem of lower image quality after replacement. Another problem associated with such a manner of replacement has been that if the surface of the photosensitive member 15 is touched by hand and its characteristic is changed or the surface is damaged, the touched or damaged part of the photosensitive member 15 becomes incapable of forming the image.
In view of the above mentioned problems, a manner of the maintenance of the apparatus has been proposed and put to practical use in which the components of the image forming section 50 are made into an integral unit or the components having similar service lives are arranged into several blocks. Thus, the integral unit or the set of the several blocks is handled as a process cartridge 51 so that the maintenance of the apparatus is carried out by replacing the process cartridge 51.
The construction of such a process cartridge 51 is explained with reference to FIG. 7. Electrophotographic process elements include a replenishment toner holding section 52, the developing device 21, the photosensitive member 15, the corona charger 20, the cleaning device 22, and a waste toner holding section 53 connected by an outer frame 54 to construct the integral process cartridge 51. As a result, such electrophotographic process elements can be replaced as a whole. The process cartridge 51 is electrically connected on one side in its longitudinal direction by a high tension connector 55 provided on the main unit side of the electrophotographic apparatus.
As seen from FIG. 8, the main unit of the electrophotographic apparatus is divided into an upper unit 3 and a lower unit 1 on both sides of the paper sheet transfer passage. The electrophotographic apparatus is constructed as an apparatus of a shell type in which the upper unit 3 can be swung to open and close about a single shaft 2 on the lower unit 1. Therefore, in the case when the paper sheet 6 is jammed, the jammed paper sheet can be easily removed by opening the upper unit 3. As shown also in FIG. 9, the replacement of the process cartridge 51 attached to the upper unit 3 is made relatively easily.
However, when the process cartridge 51 is to be removed from or mounted on the electrophotographic apparatus, an operator's hand has to access the inside of the apparatus where the high temperature fixing device 18, the transfer device 14, the developing device 21, and the high voltage discharging unit 16 are located. This poses a danger of burns and electric shocks to the operator.
Furthermore, when the process cartridge 51 is to be mounted on the electrophotographic apparatus, the mounting has to be very precise so that the connection to the high tension connector 55 is secure. This involves the possibilities of an inability to make the electric connection or further damage to the high tension connector 55 and/or connecting parts of the process cartridge 51 depending on the positional accuracy of mounting the process cartridge 51.
A further possible problem is that if the process cartridge 51 is not mounted in the specified position, the electrophotographic photosensitive member 15 hits the resist rollers, and the member 15 is damaged which leads to the lowering in quality of the image.
The process cartridge 51 is interlocked with the opening and closing movements of the upper unit 3 centered on the shaft 2. Therefore, the process cartridge also moves along an arc centered on the shaft 2 when the upper unit 3 is opened or closed. As a result, because a connector 56 on the process cartridge 51 side is connected with the high tension connector 55, as shown in FIG. 7, a cover 58 arranged around a coil 57 is slanted toward the rotation center of the upper unit 3.